Dilatation balloons are provided on the end of long catheters that can be introduced through body lumen, such as veins, arteries and other body lumens. For example, a deflated or partially inflated balloon may be positioned, such as by using optical imaging or radiological imaging, and then, the balloon is inflated to dilate the site of the lumen where it is positioned, using the force applied by hydrostatic pressure within the balloon. The balloon is deflated, and the catheter and the balloon are removed.
U.S. Pat. No. 5,163,989 is directed to a mold and method to form an inflatable member, such as a balloon for dilation catheters and the like which is free of parting lines. The mold in this reference has a continuous, unbroken inner mold surface defining a molding chamber with inner molding surface corresponding to the desired shape and dimensions for the working and tapered sections of a dilatation balloon. The mold body is made of glass or glass like material which is heat shrinkable in order to facilitate making the mold. To make shaped balloons, a tubular plastic member is placed within the inner mold chamber, inflated and heated. The plastic is pressed against the inner molding surface and is molded into the shape of the inner mold surface. The shaped balloon is cooled setting the size and shape of the balloon, and the balloon is deflated prior to removal of the balloon from the mold. The background of U.S. Pat. No. 5,163,989 disclosed uses for balloon catheters and methods used.
A mold of the type disclosed in U.S. Pat. No. 5,163,989 may be made using a variety of methods including machining, electrolytic erosion, die casting, or investment casting. Vacuum forming an inner mold surface, without parting lines, is disclosed in the detailed description of U.S. Pat. No. 5,163,989. Vacuum forming has the advantage that any shape of balloon may be made, without parting lines on the working or tapered surfaces of the balloon, which may have a smooth and continuous surface.
In order to implement vacuum forming, a heat-formable tubular member, which may be made of a glass or other material which may be softened at a glass-like softening transition temperature, is positioned around a core, which has a solid external surface shape of the desired balloon. The heat-formable tubular member is heated to a softening temperature. A vacuum is drawn internally or pressure is applied externally or both, and the tubular member collapses onto the surface of core. The tubular member is cooled below its oftening transition temperature. Then, the core is removed, such as by dissolution by a solvent. The tubular member is the inner surface of the mold and may be used to mold balloons using a parison disposed within the mold, a fluid such as nitrogen being introduced to expand a heated portion of a plastic tubular member that expands to take the shape of the inner surface of the mold.